1. Field of the Invention
The production of a semiconductor device, a printed board, a LCD and similar devices comprises an exposure process in which exposure light containing UV radiation is emitted via a mask onto a workpiece and thus a mask pattern is transferred to the workpiece. The invention relates to both a process for controlling a gap between the mask and the workpiece in a proximity exposure device and to a proximity exposure device.
2. Description of Related Art
The term xe2x80x9cproximity exposure devicexe2x80x9d is generally defined as an exposure device in which a workpiece is located at a stipulated distance parallel to a mask. Exposure light is emitted via the mask and a mask pattern which has been formed on the mask is transferred to the workpiece. During exposure, there is therefore a need for a stipulated gap between the mask and the workpiece and for a parallel arrangement of the two to one another.
FIG. 5 schematically shows the basic arrangement of a proximity exposure device. In the figures, reference letter M indicates a mask on which a mask pattern is formed and which is held securely in a mask carrier MS by vacuum suction or other securing means. Above the mask carrier MS, there is a gap measurement means 1 which is driven up and down by means of a device 2 (the gap measurement means is described for example in Japanese patent application HEI 9-75564).
A workpiece carrier WS holds a workpiece W by vacuum suction or other securing means. The workpiece carrier part in which the workpiece carrier WS is located has the multistage arrangement described below. On the base plate BP, by means of a first movement device D1 (hereinafter called xe2x80x9cZ1-movement devicexe2x80x9d), there is a first carrier ZS (hereinafter called xe2x80x9cZ-carrier ZSxe2x80x9d). The workpiece carrier WS is located on the Z-carrier ZS by means of a second movement device D2 (hereinafter called xe2x80x9cZ2-movement devicexe2x80x9d). The Z1-movement device D1 moves the Z-carrier ZS up and down.
A device for driving the Z-carrier ZS is described as follows. As is shown in FIG. 5, an intermediate movement carrier 11 is movably located over rolling components, such as balls or the like, on the base plate BP. The lower area of the Z-carrier ZS is provided with an obliquely running surface 12 at each of three locations (two of which are illustrated in FIG. 5). The obliquely running surfaces 12 are seated via rolling components, such as balls 14 or the like, on obliquely running surfaces 13 with which the intermediate movement carrier 11 is provided at the three corresponding locations.
The Z-carrier ZS is furthermore located over a bearing 16 in a guide 15 which is located perpendicular to the base plate BP. The guide 15 controls the direction of motion in the X-direction and the Y-direction such that the Z-carrier ZS does not move in the X-Y direction when it moves in the Z-direction (X: for example to the right and left in the drawings, Y: the direction perpendicular to the page of the drawing). The guide 15 controls movement in the X-direction. In the direction sloped 90xc2x0 in this respect, there is a guide which controls movement in the Y-direction.
When the intermediate movement carrier 11 is moved by a device 17 for driving the intermediate movement carrier on the base plate BP, the Z-carrier ZS moves along the obliquely running surfaces of the intermediate movement carrier 11 in the Z-direction. In doing so, the Z-carrier ZS moves only in the Z-direction because it is moving along the guide 15. Therefore it does not move in the X-Y directions. Since the obliquely running surfaces have the same slope at these three locations, the Z-carrier ZS moves in the Z-direction while maintaining the horizontal position. The movement stroke of the Z-carrier ZS is usually 50 to 100 mm.
A stipulated gap can be set between the mask and the workpiece by the parallel movement of the Z-carrier ZS in the Z-direction in this way by means of the Z1-movement device D1. Only by vertical movement of the Z-carrier ZS is it however possible that the workpiece carrier WS is sloped with respect to the exposure device, the mask and the like. Since this slope cannot be corrected by the Z1-movement device D1, there is the Z2-movement device D2 which moves the workpiece carrier WS back and forth and adjusts it. The workpiece carrier WS is supported, for example as in FIG. 5, by workpiece carrier support parts 20 at three points which each have one workpiece carrier support component 20a which can be moved in the Z-direction. The respective workpiece carrier support component 20a executes independent motion in the Z-direction by means of a drive part 20b. In this way, the workpiece carrier WS is moved back and forth, and the Z-carrier ZS is prevented from being sloped with reference to the exposure device, the mask and the like.
The workpiece carrier support component 20a of the respective workpiece carrier support part 20 is driven by means of the drive part 20b which has, for example, a servomotor. In this way, precision movement with high accuracy is achieved while the speed of movement is low. The stroke of movement of the respective workpiece carrier support component 20a is 1 to 2 mm.
The actuation of the device shown in FIG. 5 is described as follows using FIGS. 6 and 7.
(1) To simplify transport of the workpiece W in and out the workpiece carrier WS is moved down. With consideration of the thickness of a workpiece transport finger 3 and the bending of the workpiece W, a distance of at least 50 mm is required between the mask M and the workpiece carrier WS.
(2) As is illustrated in FIG. 6, the workpiece W is held securely by the workpiece transport finger 3 and is transported on the workpiece carrier WS. In the workpiece carrier part, there are transfer pins 4 (not shown in FIG. 5) in order to transfer the workpiece W between the transport finger 3 and the workpiece carrier WS. The transport finger 3 is lowered, the workpiece W is transferred to the transfer pins 4 and the transport finger 3 is removed.
(3) As is shown in FIG. 7, the workpiece carrier WS is briefly raised by means of the Z1-movement device D1 so that the distance between the workpiece W and the mask M is set to a stipulated exposure gap. By raising the workpiece carrier WS, the workpiece W is transferred to the workpiece carrier WS by means of the transfer pins 4. The above described stipulated exposure gap will be different depending on the conditions of use, the exposure process, and the other factors. But there is usually a demand for an exposure gap of less than or equal to 100 microns because the exposure accuracy (resolution) becomes higher as the exposure gap is reduced.
(4) For a parallel arrangement of the mask M to the workpiece W, the distance between the mask M and the workpiece W is measured by means of the gap measurement means 1 shown in FIG. 5 at several points (for example at three points). Based on these measured values, the workpiece carrier WS is moved back and forth and adjusted by means of the Z2-movement device D2 so that the mask M and the workpiece W are located parallel to one another.
(5) After confirming the parallel arrangement of the mask M to the workpiece W by means of the gap measurement means 1, the exposure light is emitted via the mask M and thus exposure is done.
(6) After completion of exposure, the workpiece carrier is lowered by means of the Z1-movement device D1. The workpiece W is then transferred to the transfer pins 4. The transport finger 3 is inserted into the workpiece carrier part. The already treated workpiece is transferred from the transfer pins 4 to the transport finger 3 and transported away from the workpiece carrier part.
Recently there has been a trend for workpieces to become larger. Especially in the area of liquid crystal substrates, large substrates, measuring 550 mmxc3x97650 mm to 650 mmxc3x97830 mm, are becoming more important. Furthermore there is a growing demand for an exposure gap of less than or equal to 50 microns in order to enable exposure with high precision.
When the workpiece becomes larger and the exposure gap becomes smaller, it happens with increasing frequency that the edge of the workpiece W collides with the mask M if the workpiece carrier WS is raised such that the exposure gap (for example, a distance between the mask and the workpiece of 40 microns) is achieved and when afterwards the size of the gap is measured, the workpiece is moved back and forth and parallel adjustment is done. When the workpiece W comes into contact with the mask M, problems arise that dust forms and an expensive mask is damaged.
The reason for the collision of the edge of the workpiece W with the mask M is as follows. When the individual parts of the workpiece carrier WS are mounted, adjustment takes place as follows: The workpiece carrier WS, the Z1-movement device D1 and the Z2-movement device D2 are thus subjected to a change in position vertically by the components of thin sheets, for example shims, being inserted into installation parts so that they are located parallel to the mask M.
In the parallel adjustment by one such mechanical method, however, the disadvantages are as follows. For a large workpiece carrier of a device in which large liquid crystal substrates are exposed, the labor input is considerable. There are cases in which the slope is in the 500 micron range. Furthermore, the thickness tolerance of a large glass plate is generally xc2x150 microns. When the workpiece carrier WS is moved all at once, until a gap of, for example, less than or equal to 550 microns is achieved, which is smaller than the sum of the accuracy (500 microns) for mechanical, parallel adjustment and thickness tolerance (xc2x150 microns) of the glass plate, there are therefore cases in which the edge of the workpiece W collides with the mask M. To prevent this contact of the workpiece W with the mask M, in a state in which there is a gap of greater than or equal to the above described gap (550 microns), tentative parallel arrangement is done, afterwards the gap is set smaller, and a parallel arrangement is done again. This process is repeated until the desired gap, i.e. 40 microns, is formed in parallel. But in this case, the gap measurement and measurement of the parallel adjustment must be repeated again and again. Therefore, a large amount of time for adjusting the exposure gap, and great skill for measurements and the adjustment activity, is needed.
On the other hand, in the Japanese patent disclosure document HEI 4-307550 a gap control process was proposed. Here, at a position underneath the position of the exposure gap coarse parallel adjustment is done and afterwards fine parallel adjustment at the position of the exposure gap is done.
When using the process of gap control in the Japanese patent disclosure document HEI 4-307550, however, the disadvantages are as follows for a larger workpiece W:
(1) In the embodiment described in the above described JP-OS HEI 4-307550, the position at which coarse parallel adjustment is done is defined as the position at which the distance between the mask M and the workpiece W is set to 100 microns. This two-stage adjustment consisting of the coarse parallel adjustment and the fine parallel adjustment is indeed effective when a relatively small substrate is being exposed and parallel adjustment can be done such that the mask M and the workpiece W are brought close to one another such that a distance between the two of roughly 100 microns is achieved. As was described above, for a large substrate there are cases in which the edge of the workpiece W collides with the mask M when parallel adjustment is not started at a larger gap (550 microns).
(2) Therefore, gap measurement and parallel adjustment at the position for coarse parallel adjustment, gap measurement and parallel adjustment at the position for the exposure gap and in addition gap measurement for the last check, are done several times. It is necessary to repeat these processes of gap measurement and parallel adjustment again and again. Adjustment of the exposure gap takes a long time. Furthermore skill is needed for gap measurement and the activity of parallel adjustment.
(3) The workpiece carrier has therefore been used for other purposes, besides for exposure, for a long time. As a result, the throughput of the device is adversely affected.
The invention was devised to eliminate the above described disadvantages in the prior art. Therefore the object of the invention is to provide a process for controlling a gap between a mask and a workpiece in a proximity exposure device in which there are only a few processes of measurement of the exposure gap and parallel adjustment, in which even for a large workpiece the gap between the mask and the workpiece can be controlled without contact of the workpiece with the mask, and in which no special skill is needed to adjust the gap. The object of the invention is furthermore to provide a device for executing the process.
The objects are achieved by the present invention in that, when an exposure device is being produced, the adjustment of the position of the workpiece carrier, which cannot be done solely by a mechanical method such as by shims or the like, is done by controlling the movement of the workpiece carrier.
The object is achieved by providing a device for moving a workpiece carrier composed of a first movement device and a second movement device, the latter being located on a carrier driven by the first movement device and consisting of several workpiece carrier support parts which move the workpiece carrier up and down and control its slope. The size of the gap between the bottom of a mask and the top of a workpiece located on the workpiece carrier is measured at several locations. Based on the size of the gap, the positions of the workpiece carrier support parts, when the several workpiece carrier support parts move, are recorded as a parallel zero point in a control element. The motion of the workpiece carrier support parts is executed such that the workpiece carrier is located parallel to the mask. When starting to use the device, the workpiece carrier support parts are each in a standby state after they have been moved to the parallel zero points recorded in the control element. When the workpiece is being exposed, it is placed on, and held securely to, the workpiece carrier and raised by means of the first movement device until the alignment gap position is reached. By means of the workpiece support parts of the second movement device, there is a parallel exposure gap between the mask and the workpiece and exposure is performed.
In the present invention, the process of exposure gap measurement and parallel adjustment can be reduced and, for a larger workpiece, the workpiece and the mask are prevented from contacting one another. Furthermore, parallel arrangement of the mask to the workpiece can be done without the need for special skill.